The disclosure of Japanese Patent Application No. 2000-388888 filed on Dec. 21, 2000, including the specification, drawings and abstract is incorporated herein by reference in its entirety.
1. Field of Invention
The invention relates to an engine of an automobile or other vehicle and, more specifically, to a control apparatus and a control method for a heater that heats fuel for such an engine.
2. Description of Related Art
It is known to provide an engine of an automobile or other vehicle, in which fuel is heated before being injected into a combustion chamber of the engine by heating a fuel injection valve, which injects fuel into an engine combustion chamber, using an electric heater provided for the fuel injection valve. Various devices have been proposed for improving durability of the heater by preventing it from overheating. Furthermore, various devices have further been proposed that control heating of the fuel by the heater based on temperatures of the atmosphere and the engine or combustion conditions of the fuel. Devices of this kind are disclosed, for example, in Japanese Patent Application Laid-Open Publication No. 5-288131 and 11-148441.
Japanese Patent Application Laid-Open Publication No. 7-27035 discloses a port heater that is constructed so as to heat a spray of fuel injected from the fuel injection valve from a surrounding area thereof, in which the port heater is de-energized when an engine coolant temperature reaches a predetermined value.
The engine of an automobile or other vehicle normally, when operating smoothly, starts to turn over under its own power as it is cranked for about 1 to 2 seconds by an engine starting motor. Energization of the engine starting motor is terminated after the engine has started to turn over under its own power. Depending on an engine condition and a charging condition of an accumulator device, however, it can at times happen that the engine does not start to turn over under its own power even with a cranking sequence performed by the motor until 4 to 5 seconds have elapsed. In such cases, a veteran driver would temporarily turn off a switch for the engine starting motor and, after a brief interval, try again to start the engine.
There are good reasons to take such an engine starting approach. Especially when a cold engine which has been not been operated for a long period of time is started, lubricating oil at different parts inside the engine is hard. In such a condition, it is a good idea to turn the engine over a little to allow the hardened lubricating oil to soften before using the starting motor to actively start the engine.
The same is also true with a battery or other accumulator device. Namely, it is good for the accumulator device if it is temporarily subjected to a discharge state for a short period of time so as to be ready for subsequent periods of discharge of a large current, instead of being subjected to a discharge of a surge of current to start the engine from a state in which the engine starting motor consumes a large current. In addition, an engine rotating resistance, which is increased by the hardened lubricating oil, decreases as the lubricating oil softens.
Also, a driver may occasionally stop and then restart an engine soon after it has already been started. Furthermore, it could also happen that the engine is restarted again immediately after it has previously been started depending on vehicle operating conditions, that is, the engine may be stopped while waiting for a traffic signal to change or in a traffic jam in order to save fuel resources and preserve the environment.
In an engine equipped with a fuel heating heater, on the other hand, energization of the fuel heating heater at the time of starting the engine is generally started at the same time that the engine starting motor is energized. It can therefore happen that the engine fails to start to turn over under its own power even with one cranking by the engine starting motor and, after the cranking by the engine starting motor is temporarily halted, an attempt is again made to start the engine. In this case, heat is generated additionally in the fuel heating heater, in which residual heat generated during the last session of energization for engine starting remains. As a result, the heater itself and/or fuel heated by the heater could become overheated. Such a situation can also develop when the engine is subjected to repeated short cycles of starting, stopping, and restarting.
More specifically, if the heater for heating fuel of the engine is to be provided with the fuel injection valve, the fuel injection valve is typically constructed as shown in FIG. 1. Referring to FIG. 1, a valve seat member 3 provided with a fuel injection hole 2 is installed in an inner portion on a leading edge of a metallic valve body 1 having a cylindrical shape. There is disposed movably in an axial direction, a needle 4 inside the valve body 1, being guided concentrically with respect to the valve body 1 by an annular needle guide 5 of an annulus wavy metallic sheet. A valve head portion 6 at a leading edge of the needle 4 therefore opens and closes the injection hole 2. The needle 4 is a hollow tubular member except for the valve head portion 6. That part of fuel sent through the needle moves past a hole 7 to flow over an area around the valve head portion 6. Meanwhile, that part of fuel that flows through an annular passage formed between the needle 4 and the valve body 1 along the needle guide 5 moves past a hole 8 to temporarily flow into an inside of the needle 4. It thereafter flows over the area around the valve head portion 6 through the hole 7 and, when the valve head portion 6 leaves the injection hole 2 of the valve seat member 3, is injected through the injection hole 2. There is disposed movably along an axis of the valve body 1 on an inside at a root portion of the valve body 1 an armature 9 that is connected to a trailing edge of the needle 4. An electromagnetic coil 10 that, when energized, drives the armature 9 to the right in the figure is provided on an outside of the root portion. A compression coil spring 11 urges the armature 9 together with the needle 4 toward a valve closing position to the left in the figure.
A heater 12 that heats fuel is secured by a heater holder 13 around the valve body 1. A base portion 15 made of heat-resistant resin is formed through mold forming by way of a heat-resistant rubber ring at a trailing edge of the heater holder 13. The fuel injection valve equipped with a heater is mounted on an intake port portion 17 of a cylinder head through an insulation ring 16 made of heat-resistant resin.
In the fuel injection valve equipped with a heater and a mounting structure thereof, heat generated through energization of the heater 12 is transferred through heat conduction to the valve body 1, a major portion of which is made of metal. The heat is then transferred from an inner wall of the valve body 1 and the annular needle guide 5 in contact therewith to the fuel that flows through the annular passage formed between the inner wall and the needle 4 along the needle guide 5. At the same time, the heat is further transferred through the needle guide 5 to the needle 4 and eventually to the fuel that flows inside the needle 4. In this manner, fuel is heated before being injected from the injection hole 2.
Part of the heat transferred to the valve body 1 is transmitted from the root portion of the valve body 1 through a housing 18 of the electromagnetic coil 10 to the base portion 15 made of molded resin. Part of the heat generated by the heater 12 is also transmitted to the base portion 15 through the heater holder 13 and the heat-resistant rubber ring 14. Since the base portion 15 is not in direct contact with the intake port portion 17 of the cylinder head, the heat transmitted to the base portion 15 flows, being transmitted therethrough, toward an extended portion on the right in the figure and eventually undergoes heat conduction. Since resin has a low thermal conductivity, however, the temperature of the base portion 15 of the molded resin is the highest at a leading edge portion thereof adjacent to the heat-resistant rubber ring 14 and the electromagnetic coil housing 18. If the temperature at this portion becomes too high, it could overload the base portion 15.
The fuel heating heater, which is provided with the fuel injection valve in the above example, may be provided at the intake port portion so that it heats a jet of fuel injected from the fuel injection valve. In either case, however, the heat once loaded on the heater must be transferred to the heater supporting portion and diffused in the surrounding atmosphere unless it is taken away by fuel or an intake air flow. This requires a large amount of time.
If heating by the heater 12 goes beyond a required level, it could vaporize a top portion of fuel. This vaporization process could cause fuel vapor to adhere to the areas around the holes 7, 8 thus making them narrower or plugging them up, resulting in what is called vapor lock.
In view of the foregoing problems involved with the fuel heating heater for an engine, it is an object of the invention to even further improve control of operation of such a heater. More specifically, a heater control apparatus according to one aspect of the invention (i) determines an operation time of the heater in a most recent operation of the heater, (ii) determines an elapsed time since the heater has been stopped, and (iii) controls the operation of the heater based on the determined operation time and elapsed time. A heater control method according to one aspect of the invention determines the operation time of the heater in a most recent operation of the heater and determines the elapsed time since the heater has been stopped and, based on these determined times, controls the operation of the heater.